Reverse conducting insulated gate bipolar transistors (RC-IGBTs) function as IGBTs with a monolithic integrated antiparallel diode. In case of n-channel RC-IGBTs, a p-doped emitter at a rear side electrically coupled to a collector terminal is interrupted by highly n-doped regions acting as emitter shorts between a drift zone and an electrode at the rear side.
In a power semiconductor transistor such as an RC-IGBT an active area including transistor cells connected in parallel is surrounded by a junction termination structure. In a blocking mode of the IGBT the junction termination structure reduces an electric field in a lateral direction from the transistor cell array to a chip edge.
One goal of development of new generations of RC-IGBTs lies in a shrink of an active chip area while maintaining or improving chip functionality. A shrink of active chip area is accompanied by a shrink of a total area of the monolithic integrated antiparallel diode leading to an increase of a forward bias voltage at a reference current. A similar impact may be caused by a reduction of a thermal budget after processing a rear side emitter and the emitter shorts. The functionality of the monolithic integrated antiparallel diode may also be affected by a voltage applied to a gate electrode of the RC-IGBT in a forward bias mode of the monolithic integrated antiparallel diode. Depending on an implementation of an RC-IGBT, a gate voltage of an n-channel RC-IGBT may be positive in a forward bias mode of the monolithic integrated antiparallel diode. In this case, a field effect transistor (FET) channel may be turned on leading to a discharge of electrons injected by the emitter shorts acting as a cathode of the monolithic integrated antiparallel diode. Discharge of these electrons via the channel suppresses bipolar gain by a p-doped body region acting as an anode of the monolithic integrated antiparallel diode. Again, an increase of a forward bias voltage at a reference current may result leading to an increase of conduction losses of the antiparallel diode.
There is a need for a RC-IGBT, which, among other advantages and features, exhibits an improved trade-off between conducting and switching losses.